High pressure piston pump for liquefied gases



Dec. 31, 1957 I B. PETZOLD 2,313,029

HIGH PRESSURE PISTON PUMP FOR LIQUEF'IED GASES Filed April 24, 1953 United States PateiitU HIGH PRESSURE PISTON PUMP FOR LIQUEFIED GASES Application April 24, 1953, Serial No. 350,865

Claims priority, application Germany May 2, 1952 3 Claims. (Cl. 103-178) This invention relates to high-pressure piston pumps for the conveyance of liquefied gases.

It is an object of the invention to provide a pump of this type which is more efficient in action than other pumps hitherto used for the same purpose and which is free from certain deficiencies which cause these pumps to become occasionally inoperative.

In piston pumps as hitherto used for the conveyance of liquefied gases the piston reciprocates in a cylinder formed with intake slots controlled by the piston, the liquefied gas being sucked in through these slotswhich are covered and held closed by the piston during the pressure stroke and the major part of the suction stroke and are uncovered shortly before the end of the suction stroke. The liquid is then free to enter the cylinder until the piston during its return stroke starts covering the slots again and then goes through the pressure stroke. When the pressure stroke has ended, the dead space in the cylinder is filled with liquid acted upon by the expulsion or counter-pressure, and when the piston starts on its return stroke, the liquid, owing to the increase in volume, as the pressure continues dropping, is partly vaporized. At the moment where the piston uncovers the intake slots, the cylinder is filled with gas and some remaining liquid, both of them under a pressure lower than the suction pressure, so that now the liquid to be conveyed rushes into the interior of the cylinder. In consequence of the rise of pressure thus created part of the gas phase is condensed, however, some gas will remain in the cylinder and in the end will hinder the inflow of fresh liquid. When the slots have been covered completely by the piston, the cylinder is filled with liquid and with the gas which remained over in the cylinder, and this gas will be compressed and condensed again before the conveyance of liquid against the expulsion pressure can start again.

The facts here recited constitute a serious drawback in that the formation of vapor during the suction pressure renders it impossible to fully take advantage of the volume presented by the cylinder in conveying the liquid.

Another drawback arises from the fact that the known pumps are fitted with pistons which are solid all through and therefore take more time to cool down, when the pump starts operating, than the cylinders, because the liquid enters the pump from the outside and comes into contact with the cylinders first. This circumstance causes the play between the piston and the cylinder to be reduced to such an extent that the piston is likely to get stuck in the cylinder.

I have now found that all these drawbacks can easily be avoided by providing the pump with a hollow piston which is separate from, and not connected with, the piston rod, the piston and the piston rod being capable of some relative movement in the radial sense and of a short movement in the axial direction as compared with the length of the piston, the piston being guided by the cylinder, the piston rod by the casing.

The piston rod, before taking the piston along on its ice suction stroke, first moves from its dead center position following its return from the preceding pressure stroke through the distance separating it from the piston and across the intake slots and by means of a head attached to it and forming a valve slide pushes the liquefied gas entering the piston through the slots into the cavity of the hollow piston. The slide head, having a greater diameter than the cavity of the piston, on meeting the piston closes the cavity and pushes the piston with the liquid filling it toward the pressure end of the pump, while the liquid still in the dead space has no opportunity to vaporize. At the end of the suction stroke the hollow piston first stays put, while the rod starts on its return stroke, its slide head covering the intake slots before the rod takes the piston along. The flowing in of the liquid through the cavity in the hollow piston into the cylinder is not accompanied by any undesirable vacuum or evaporations and the cylinder is filled to a high extent. Any sticking of the piston on starting moving is avoided owing to the fact that the cold liquid entering the cylinder first contacts the hollow piston, then enters it through the in take slots and only at the end of its movement fills the cylinder in contacting its body.

In the drawings affixed to this specification and forming part thereof an embodiment of this invention is illustrated diagrammatically by way of example in an axial section.

Referring to the drawing, 1 is an inlet for supply of fluid to the pump casing 2, within which there is located a suction chamber 3 to which the inlet 1 leads, said suction chamber communicating with the pump casing 2. A pump cylinder 7 extends from suction chamber 3 to the wall of pump casing 2, a discharge opening in the pump casing wall forming the discharge end of the cylinder, and a check valve 9 is located in the discharge opening of the cylinder. A hollow piston 4 is positioned to reciprocate within the cylinder 7, and the piston includes a portion which remains outside the cylinder during the reciprocal movement of the piston. A recess is located as shown in the drawing in the interior wall of the portion of the piston which remains outside the cylinder, and an intake slot 6 is located in this recess, the intake slot being in communication with suction chamber 3. The portion of the hollow piston lying within the cylinder is open ended to permit flow directly into the cylinder. A piston rod 5 has a flange 8 on the end thereof nearest the cylinder, said flange being displaceable axially between checks or stops 11 and 15 formed by the opposite ends of the recess in which the flange moves, the movement of the piston rod and flange thereon thereby serving to control passage of fluid through the intake slot or slots and the intake portion of the hollow piston, and also to reciprocate the piston within the cylinder by the pressure of the respective faces of the flange against the checks or stops 11 and 15. A discharge outlet 10 is located beyond the check valve 9. Pump casing 2 is provided with a vent 13 leading from the interior 12 of the pump casing.

On leaving its dead center position shown in the drawing the slide 8 thus moves first through a certain distance past the intake slot 6. Since the slide 8 also tightly closes the rear end of the piston 4, the liquid in the piston cavity serves as a pressure piston and together with the piston 4 forces the liquid in the cylinder 7 past the check valve 9 into the high pressure pipe 10. Once the left-hand dead center position has been reached, the entire liquid in the cylinder 7 is forced through the valve 9 save an unavoidable small quantity in the dead space and any leakage losses which may have occurred. On the other hand, the column of liquid still fills the hollow piston. On starting its suction stroke, the slide 8 first moves toward the right and in doing so uncovers the intake slots 6.

Patented Dec. 31,, 1957 As soon as the slide 8 meets its check 11, it carries the piston along and the space within the piston and the cylinder is filled with entering liquid and no opportunity is given the liquid for evaporation. The liquid flows in steadily until the right-hand dead center position has been reached. Only within the entrance. space 3 and the casing 12 a slight quantity of liquid can evaporate and the gas can escape through the vent 13.

I wish it to be understood that I do not desire to be limited to the details of construction described above and shown in the drawings for obvious modifications will occur to a person skilled in the art.

I claim:

1. In a high pressure piston pump for liquefied gases including a cylinder, a check valve located in the discharge opening of said cylinder, a hollow piston positioned to reciprocate within said cylinder, said piston including a portion remaining outside the cylinder during its reciprocal movement, and a piston rod for moving said piston,

in combination, a recess in the interior wall of the portion of the hollow piston remaining outside the cylinder during its reciprocal movement, stops formed by the ends of said recess, an intake slot located in said recess, and a flange on the end of the piston rod nearest the cylinder, said flange being displaceable axially between said stops formed by opposite ends of said recess, said flange serving to control passage of fluid through said intake slot and the intake portion of the hollow piston, and to reciprocate said piston within the cylinder.

2. A high pressure pump for liquefied gases comprising, in combination, a pump cylinder, at check valve located in the discharge opening of said cylinder, a hollow piston positioned to reciprocate within said cylinder, said piston including a portion remaining outside the cylinder during its reciprocal movement, a recess in the interior Wall of the portion of said piston remaining outside the cylinder,

located in said recess, a piston rod having a flange on the end thereof nearest the cylinder, said flange being displaceable axially between said stops formed by opposite ends of said recess, the movement of said piston rod and flange thereon serving to control passage of fluid through said intake, slot and the intake portion of the hollow piston, and to reciprocate said piston within the cylinder.

3. A high pressure pump for liquefied gases comprising, in combination, a pump casing, a suction chamber located within and communicating with said pump casing, an inlet connected to and for supply of fluid to said suction chamber, a pump cylinder extending from said suction chamber to the Wall of said pump casing, a discharge opening in the pump casing wall forming the discharge end of the cylinder, a check valve located in said discharge opening, a hollow piston positioned to reciprocate within said cylinder, said piston including a portion remaining outside the cylinder during its reciprocal movement, a recess in the interior wall of the portion of said piston remaining outside the cylinder, stops formed by the ends of said recess, an intake slot located in said recess, a piston rod having a flange on the end thereof nearest the cylinder, said flange being displaceable axially between said stops formed by opposite ends of said recess, the movement of said piston rod and flange thereon serving to control passage of fluid through said intake slot and the intake portion of the hollow piston, and to reciprocate said piston within the cylinder, and a discharge outlet located beyond said check valve.

7 References Cited in the tile of this patent UNITED STATES PATENTS 574,915 Lamplough Jan. 12, 1897 

